Web and tape guiding apparatus guide magnetic or optical tape over a read/write head. Guiding the tape over the head is critical to the writing of data to and the reading of data from the tape. A typical magnetic tape drive includes several elements in the tape path to ensure proper alignment and operation of the tape and the head. For example, the tape path of a typical tape drive may include a supply reel, a vibration decoupler, a cleaner blade, a magnetic read/write head, a tension transducer, a storage reel, and tape guides.
The tape guides physically align the lateral position (i.e., in the direction of the tape width) of the tape relative to the read/write head. Lateral positioning maintains proper alignment between the read/write elements of the head and the data tracks on the tape. The tape guides also support and guide the tape in its easy direction of bending (i.e., in the direction of tape travel).
Three basic types of guides are known for easy direction tape guiding. The first guide type is a fixed cylindrical post. A fixed cylindrical post is based on theory that a hydrodynamic film of air forms between the tape and the post when the tape is in motion, thereby reducing friction and wear. However, practically sized posts fail to produce an air film of sufficient thickness to reduce friction and wear to a significant extent. Also, when the tape is stopped and rests on the post under tension it sticks to the post. Such stiction makes the initiation of tape movement difficult and may result in damage to the tape or tape drive failure due to the inability of the tape drive to start tape motion. Stiction is especially a problem with posts in hot and wet environments.
The second guide type is a roller. As compared to posts, rollers reduce friction with a tape in motion and stiction with a tape at rest because rollers are always rotating while a tape is in motion. However, rollers introduce vibration into the tape path (which may disrupt the head-tape interface). Also, rollers store energy that must be positively controlled to maintain adequate closed loop tension control. Rollers steer tape differently than do posts, and often require grooves or other geometries to prevent the tape from flying over and above them. Further, rollers employ expensive ball bearings.
The third guide type is an externally pressurized air bearing. Although an air bearing can dramatically reduce tape friction and stiction, it is more complex and expensive than a post or roller. An air bearing is complex because it requires the space and parts for air to be provided under controlled pressure.
Examples of fixed cylindrical posts and/or rollers are disclosed in U.S. Pat. Nos. 4,633,347, 4,341,335, 4,144,991, 3,991,956, 3,360,174, 3,276,651, and 3,327,964. To the extent that these references disclose the guiding of tapes, the posts and/or rollers are used to drive tape movement, control tape tension, or provide lateral tape guiding. Also, U.S. Pat. No. 4,071,177 discloses air bearings and U.S. Pat. No. 4,276,575 discloses the use of a plastic lubricant on a tape guide to reduce friction. Examples of other guides are shown in U.S. Pat. Nos. 5,289,331 and 5,282,105.
What is needed is a tape guide that has the advantages associated with fixed cylindrical posts and rollers without the disadvantages associated with these types of tape guides.